Epidural analgesia has been established as the “gold standard” for pain relief in labor. However, there are many parturients who do not receive it either due to medical contraindications or personal refusal. As a corollary, there are many who are unwilling or uncomfortable with having an epidural needle inserted in their backs for fears of side effects and complications. Indeed, epidural analgesia may be unsuitable or contraindicated for some, including those with severe back problems. Epidural analgesia may also be deemed unsuitable for some who are in pain but may be in ‘spurious’ labor as well as those who are in late labor for which there might not be enough time for a fully effective epidural pain relief to be established. In some situations, an epidural may not be fully effective and some other modality of pain management may be required.
Currently, the other methods of providing pain relief involve principally the use of a gas mixture called entonox or an injection of an opioid into the muscle or vein. These methods have not been found to be effective apart from producing side effects. Similarly, epidural anesthesia during a cesarean section may require additional medication to render a greater quality of pain relief.
There have been some recent developments on the existing treatment options. For example, the use of intravenous (IV) remifentanil, a fast acting opioid that has seemingly minimal long term effects due to the favorable pharmacokinetic profile, has gained much popularity in the context of treatment for labor pain. Intravenous drugs could be administered via a patient-controlled modality, whereby the patient pushes a button to trigger the administration of drug intravenously when pain is felt by the patient (Sia et al., Singapore Med 1, 2006, 47, 951-956; Hinova et al., Anesth Analg., 2009, 109, 1925-1929).
In recent years, patient-controlled analgesia (PCA) using the synthetic opioid remifentanil has been used with some success as an alternative to epidural analgesia, conferring moderate analgesia especially in early labor. As with other opioids, the use of remifentanil is also limited by known maternal side effects which include bradycardia, sedation and respiratory depression.
Despite the recent use of patient-controlled intravenous remifentanil administration which appears to be superior to many other modalities of treatment (Leong at al., Anesth Analg., 2011, 113, 818-825) and is considered a good alternative to epidural analgesia, the optimal infusion regimen in this respect is still contentious. This is because labour pain is intermittent and it escalates as labour progresses. Therefore, the doses used would be correspondingly and incrementally larger as labour progresses. Moreover, there is often a lag time before the full effect of a particular dose effectively kicks in. The use of remifentanil is associated with the common side effects of opioids albeit transient due to its non-accumulative and rapid effect. However, some side effects, such as respiratory depression, would be sinister and should be prevented at all costs. Another potential side effect is the fetus' reaction to the drug which could manifest as an adverse fetal heart rate (slowing, a loss of reactivity or deceleration).
Therefore, there is a need to provide for a patient-controlled analgesia methodology with enhanced efficacy, safety and personalization of pain relief therapy with minimum side effects.